Aerial survey

ABSTRACT

A target positioning device has a closed circuit television system on a helicopter, the system having a camera arranged to view the terrain below the helicopter and a viewing console for displaying an image of the terrain to the pilot. A laser and a laser detector of which one is on the ground and the other on the helicopter, are used to indicate to the pilot whether the helicopter is accurately vertically aligned with a predetermined point on the terrain.

United States Patent [191 McConnell et al.

[ AERIAL SURVEY [75] Inventors: Frederick C. McConnell; George Jason;Neil J. Armstrong, all of Calgary, Alberta, Canada Spartan Air ServicesLimited, Ottawa, Ontario, Canada Filed: Aug. 11, 1972 Appl. No.: 279,792

Related US. Application Data Division of Ser. No. 65,259, Aug. 19, 1970,Pat. No. 3,709,607, which is a continuation of Ser. No. 817,448, April18, 1969, abandoned.

Assignee:

US. Cl 178/6.8, 356/4, 356/152, 250/203 R, 244/l7.11

Int. Cl. G01b 11/26 Field of Search 356/4, 5, 141, 152, 356/172, 138;250/203 R, 215; 244/l7.1l, 17.17; 33/1 T; 178/6.8

References Cited UNITED STATES PATENTS 9/1971 SmithVaniz ..356/1528/1970 Atteberry et a]. ..244/17.l1

5C BEE/12 Primary ExaminerSamuel Feinberg Assistant Examiner-S. C.Buczinski Attorney-Harvey Kaye [5 7] ABSTRACT A target positioningdevice has a closed circuit television system on a helicopter, thesystem having a camera arranged to view the terrain below the helicopterand a viewing console for displaying an image of the terrain to thepilot. A laser and a laser detector of which one is on the ground andthe other on the helicopter, are used to indicate to the pilot whetherthe helicopter is accurately vertically aligned with a predeterminedpoint on the terrain.

17 Claims, 3 Drawing Figures 7 7'1/ CAME/PA AERIAL SURVEY CROSSREFERENCE TO RELATED APPLICATION This application is a divisional ofapplication Ser. No. 65,259, filed Aug. 19th, 1970, now US. Pat. No.3,709,607 which itself is a continuation of Ser. No. 817,448, filed Apr.18th, 1969, and now abandoned.

This invention relates to target positioning apparatus for use in aerialsurveying.

Surveying has for many years been one of the most important aspects ofmining, petroleum or other field operation, and it is a time-consumingprocedure. All surveys rest primarily on linear measurements for thedirect determination of distances. in non-wooded, accessible areas,surveying has historically been carried out by surveyors using transitsand stadia poles. Often the system of surveying known as triangulation(which utilizes the simple geometrical principle that if one side andtwo angles of a triangle are known, the measurements of the rest of thetriangle can be computed) is used. Thus, linear measurements may besupplemented by angular measurements. This enables distances to bedetermined over areas which cannot be measured directly, as, forexample, hilly or broken ground.

In wooded areas and in relatively inaccessible areas, both distance andangle measuring devices (transits and theodolites) placed at groundlevel cannot be used. Accordingly, it has been the practice to build atower on top of which sits a slave or master station, thus giving a lineof sight above the treetops for twenty to thirty miles distance. Aportable steel observation tower, as for example that known under thetrade name Bilby Tower, has frequently been used. Such an observationtower is like a giant tripod, extensible to over 100 feet, and isprovided with an inner tripod which holds the transit or theodolite, butdoes not vibrate at the movements of the surveyors who stand on theseparate outer tower. The task of building or erecting such towers inremote areas has been facilitated in recent years by the use ofhelicopters, which can transport both the men and the materials.

However, the building or erecting of such towers is an expensive andtime-consuming task. Consequently it has been suggested that thehelicopter could be used as a sighting target, if it could hoveraccurately over a point on the terrain. The practical success of such aproposal depends upon: firstly, the provision of accurate means ofmeasuring the distance from a fixed point (in line of sight with anddistant from the helicopter) to the helicopter; secondly, the provisionof sufficient hovering accuracy for the helicopter; and thirdly, theprovision of a satisfactory hover sight.

The first problem has been solved by use of a tellurometer, which is adistance measuring device utilizing line-of-sight radio waves. It is, ineffect, a two-way radio telephone system which operates between a masterunit and a remote unit. The second problem has been solved by provision,in the helicopter, of a stability augmentation system which allows for amore accurate hovering technique.

It has been suggested to solve the third problem and also to provide anaccurate surveying system and technique that the following procedure beutilized. A heli copter is fitted with a vertical rod (like a stadiapole) located at the centre of the top of the helicopter. Also installedin the helicopter and precisely located in the centre bottom of themachine is a plumb bob on a string, attached to a drum mechanism, formeasuring the distance of the helicopter above the ground. By lookingthrough a series of mirrors located in the pilot's compartment of thehelicopter, the pilot can see the string and plumb bob and a stationmark below him. The pilot can raise or lower the helicopter toaccommodate the height of the trees. He can also manoeuvre until theextended plumb bob is located exactly over the station mark. He can thenattempt to hold the helicopter in this fixed position while anothermember of the survey crew, using a tellurometer, takes a reading on thevertical pole attached to the top of the helicopter. The helicopter mayalso have attached to the top thereof a Grimes beacon or a strobe light,in order that the general direction could be determined by thetellurometer operator in the distance. The height of the helicopter ismeasured by calibrating the plumb bob string. The pilot and thetellurometer operator are in radio contact so that the pilot can informthe operator when the plumb bob is precisely over the station mark' in aposition for a reading to be taken.

While this system and procedure has proven fairly accurate, it is quiteexpensive. Furthermore, the accuracy is impaired by the fact that windand turbulence created by the helicopter may have an effect on thestability of the plumb bob line. Consequently, the stadia pole atop thehelicopter may not be along a line exactly vertical to the station mark.

It has also been proposed to provide a television camera on ahelicopter, the television camera being mounted in a pendulum-likemanner so that the optical axis of the camera will always assume avertical position. A monitoring television receiver in the helicopterenables the pilot to cause the helicopter to hover in a position above agiven point on the ground. The camera may include a zoom lens andappropriate filters to overcome the effects of inclement weather.However, this arrangement has the disadvantage that the pilot has toadjust the zoom lens in addition to his normal piloting functions as heapproaches a position above the point on the ground, and to readjust thezoom lens if he inadvertantly manoeuvers into a position in which thepoint is no longer in the field of view of the camera, which addsconsiderably to the tasks which-the pilot has to perform, particularlywhen this operation is carried out under conditions of poor visibility.

It is accordingly an object of the present invention to provide a noveland improved target positioning apparatus for use in aerial surveyingwhich mitigates the above disadvantages.

It is a further object of the present invention to provide a targetpositioning apparatus for use in aerial surveying which employs atelevision system to assist a helicopter pilot to locate a point on theground and a laser beam to enable him to position the helicopter moreaccurately above that point.

According to the present invention, a target positioning apparatusemploys a television camera and a viewing console mounted on ahelicopter and arranged to provide for the pilot a television image ofthe terrain beneath the helicopter. In addition, a laser and a laserdetector are provided, one on the helicopter and the other on the groundso that the pilot can tell when his helicopter is correctly positionedby ascertaining whether the laser is vertically aligned with the laserdetector.

It has been found advantageous in some circumstances to utilize aclosed-circuit television system in which the camera is mounted in thehelicopter by means of well-lubricated gimbal rings such that the camerais free to maintain an attitude substantially vertical to the earth whenthe helicopter is airborne. Also, the television console with viewingscreen is best located adjacent the instrument panel of the helicopterwhere it can be seen easily by the pilot. In such practice of thisinvention, the laser may be mounted on the television camera which iskept vertical to the earth; the laser projecting a beam onto the terrainfor viewing from the helicopter. Alternatively, as mentioned in thepreceding paragraph, the laser can be positioned over the point in sucha manner as to project a laser beam vertically upward from the point. Alaser beam detector mounted on the helicopter indicates when thehelicopter is accurately positioned over the point.

Another feature of the invention is the provision of a control andactuating mechanism responsive to the detection of a laser beam, whichmechanism can be utilized to aid in the operation of survey apparatusand in the accurate positioning of the helicopter over the point.

In order to take the desired survey measurements distance measuringequipment normally is associated with the helicopter, for example,horizontal distance measuring equipment such as autotape or tellurometerposition fixing devices. Further there is usually a height measuringdevice also associated with the helicopter which is capable ofaccurately determining the distance between the hovering helicopter andthe point on the ground beneath. This device may be, for example, acalibrated, spring-loaded plumb bob and reel.

If desired, the laser beam detector can be utilized to activate certainpreselected mechanisms associated with the helicopter upon detection ofthe laser beam projected vertically upward. It can be used, for example,to automatically activate the horizontal distance measuring equipment.The detector can comprise plural detection cells, at least one such cellindicating that the helicopter is positioned accurately over the point,and at least another of the cells indicating when the helicopter hasdrifted such that it is not positioned over the point. The differentcells can be used to activate and positively deactivate the distance andheight measuring device. The plural cells of the laser beam detector canbe arranged in the form of two concentric rings of cells in order tooperate as outlined above.

Therefore, the present invention provides a control and actuatingmechanism which is particularly suited to use in survey work, althoughit can find application in other situations wherein a laser beam isutilized and reference is made thereto for actuation and control ofother equipment. The mechanism includes a laser beam receiver with firstmeans for sensing a predetermined desired condition and in response tothe presence of that condition for initiating operation of a preselectedmechanism, and second means for sensing a predetermined undesiredcondition and in response thereto discontinuing operation of apreselected mechanism. In a preferred embodiment, the control andactuating mechanism utilizes a laser beam detector having pluraldetection cells. A first cell upon sensing the presence of a desiredcondition initiates operation of a preselected mechanism. A second cellupon sensing the presence of a predetermined undesirable conditionpositively discontinues operation of a preselected mechanism.

As an example, if the control and actuating mechanism is mounted in ahelicopter for use in survey work, the desired condition can be met whenthe hovering helicopter is accurately positioned vertically above apoint on the terrain, and the undesired condition may be achieved whenthe helicopter is no longer accurately positioned over that point.Consequently, when the first means in the laser beam receiver, Le. afirst detection cell, senses the laser beam and that therefore thehelicopter is accurately positioned over the survey point, the distancemeasuring devices and the Grimes beacon or strobe light can be activatedand their operation commenced. When the second means in the laser beamreceiver, i.e. the second detection cell, senses that the helicopter hasdrifted, i.e. is no longer accurately positioned over the station mark,the operation of the distance measuring devices and the Grimes beacon orstrobe light can be terminated.

Another example of the actuation of a preselected mechanism would be therelease of the plumb bob reel mechanism when the helicopter isaccurately positioned over the survey point, so that the perpendiculardistance of the helicopter over the survey point at that time can bemeasured.

The helicopter preferably is one which is equipped with a stabilityaugmentation system, which aids in a more accurate hovering techniquethan may be otherwise possible. One such helicopter is known under thetrade name Hiller model SL4, and is manufactured by the HillerHelicopter Company. Another such helicopter is the Bell 47 model 3Blhelicopter.

The laser can be attached to any normal instrument, and in the presentinvention, it is a portable laser preferably of the type known as atransit-laser. The inherent characteristics of a laser, namely theemission of an intense beam of coherent light (red in colour in a rubylaser) which is clearly visible either at night or in daylight, are usedto advantage. Since the laser beam remains essentially parallel and doesnot expand as it travels over long distances, the laser beam isanalogous to an endless, weightless, stretched string which is visibleover a great distance. It becomes, in effect, a clearly visiblereference line.

A transit-laser beam is clearly visible on a target one thousand feetaway as a spot whose centre can be judged to within about 56 inch.Simple detectors (for example goggles) are available, which by filteringout extraneous light in effect permit greater viewing range. Inaddition, the operator may use a retroreflector which will pick up thebeam at a substantial range allowing the operator to know whether or nothe is constantly on target. Should his instrument be jarred for anyreason, the retroreflector will make him aware that such has happened.At night, the transit-laser beam is visible for a distance of up toabout ten miles. One commercially available laser which may be used inthe practice of this invention is known as the University LaboratoriesModel 610 transit-laser.

The means associated with the helicopter for the taking of distancemeasurements may be simple or sophisticated. One such simple means is asight light by which transit readings may be taken from two knownlocations. Alternatively an autotape or a position-fixing device such asthe model MRB3 of Tellurometer Canada Limited may be used; these devicescan be adapted to be activated electronically by a laser detector. Uponreception of the laser beam, the laser detector then activates theautotape or the MRB3 which automatically takes distance readings onremote units located at known locations.

The closed-circuit television system which can be used in the variousaspects of this invention preferably is one which has high resolution,even under the conditions of vibration and other problems associatedwith helicopter operation, in order to provide a clear picture. One suchcommercially available system is manufactured under the brand name ofSony closed circuit television set.

The camera of the closed circuit television system in one embodiment maybe mounted pointing down and ahead through the tail boom of thehelicopter. The viewing console of the television system normally isplaced in front of the rudder pedals of the helicopter and is used bythe pilot to enable him to face his instrument panel and still be ableto see underneath his machine, thus facilitating his hovering over afixed point. The closed circuit television system enables the helicopterto hover over a station mark and to obtain a fix over such station mark.In another embodiment, the television camera preferably is mounted onwelllubricated and ball-bearinged gimbal rings. Thus, regardless of theattitude of the helicopter, the camera is free to move so that it isperpendicular with the ground at all times when the helicopter isairborne.

In a preferred embodiment of the present invention, a laser beamdetector is mounted on the helicopter, a good position being in front ofthe vertically directed television camera lens. The laser detector may,for example, be a single cell, or preferably may consist of twoconcentric rows of laser beam sensitive cells. These rows of cells canbe used to activate preselected mechanisms mounted on the helicopterupon reception of the beam from the laser mounted over the station markbelow.

In a second embodiment of this invention, the laser can be mounted onthe helicopter so that the laser beam is centrally located in line withthe television set on the helicopter and is always pointing verticallydownward. In this way the pilot can see, by means of the closed circuittelevision set, the positioning of the helicopter by observing the laserbeam with respect to the station mark on the ground below.

It is an additional advantage in the practice of this invention that atape recording of the television operations can be made and preserved.This tape recording could be reviewed later, after the field work iscompleted, should it be necessary to check the survey results.

The laser beam is used to provide an accurate positioning of thehovering helicopter over a station mark. The accurate measurement of thehelicopter height would normally be carried out by using a plumb bobstring attached to a calibrated drum. When the plumb bob touches thestation mark, the exact height above the station mark can be read.

It is to be observed that reference has been made to a station mark.Other well-known survey points, such as bench marks, triangulationstation marks, traverse station marks and corner monuments, azimuthmarks, etc. are also interchangeable with station marks, and indeed, anypoint whose position it is desired to fix at a given time may bedesignated as a station mark.

Reference now will be made to the accompanying drawings which willillustrate the practice of the invention according to one embodimentthereof:

FIG. 1 is a schematic view of a helicopter hovering over a station markundertaking survey work from the air.

FIG. 2 is a view in more detail of the instrumentation utilized in thesurvey method shown in FIG. 1; and

FIG. 3 is a schematic electrical diagram of the control and actuatingmechanism and associated instrumentation, utilized in the practice ofthis invention in conjunction with the equipment illustrated in FIG. 2.

FIG. 1 shows a hovering helicopter 10 (which may be a Bell 47 model 3B1helicopter) hovering over a station mark 11, namely a point whoseposition it is desired to locate. The helicopter is provided with aheight measuring device 12, which in the embodiment shown includes aplumb line 13 and a plumb bob 14. Alternatively, although not shown, thehelicopter may be provided with a stadia rod incorporated in the bottomthereof which can be read through a telescope on the ground to obtainthe measure of the vertical height of the helicopter above the stationmark. The helicopter is provided with a laser detector 16 mounted on theleft cargo rack. The detector 16 is adapted to receive the laser beamprojected by a laser 25 situated over bench mark 11. Directly above thedetector 16 is the lens of a television camera 17, the screen 19 ofwhich is mounted adjacent the helicopter instrument panel 18. Directlyabove the television camera 17 is a sight light 20, which may be aGrimes beacon or a strobelite. This equipment is used to locate thepoint at station mark 1 1 in the horizontal plane.

As seen more clearly in FIG. 2, the altitude measuring device 12includes a plumb bob l4 and reel 30, the reel being calibrated andspring loaded, and provided with a weight sensitive indicator. Thespring release in the system records the instant that plumb bob 14touches the terrain, thus giving the vertical height of the calibrateddrum 30 above the station mark 11.

Over station mark 11 is a tripod 21, on the bench 22 of which is mounteda level 23, a vertical telescope 24, and a transit-laser 25. The laserdetector 16 includes a dome 26 provided with two internal concentricrows of laser beam sensitive cells 27 and 28, which may be photovoltaicor photoresistance cells. The lens 29 of .television camera 17 is indirect vertical line with the laser detector 16. The instrument panel isalso provided with indicator lights 31 to be more fully described withreference to FIG. 3.

While not shown in FIG. 2, the rows 27 and 28 of laser beam sensitivecells may be coupled to the sight light and to the electronic distancemeasuring equipment, e.g. an autotape or position fixing device known asmodel MRB3 of Tellurometer Canada Limited. The measuring means could beactivated when the detector 16 receives the beam of the laser 25; thusautomatic distance readings may be taken on two remote units, onelocated at each of two known locations.

FIG. 3 schematically illustrates the electrical. circuit diagram. Apower supply 32 is operatively connected to the dome 26 of the laserdetector, to an on/off switch 33 and thence to a distance measuringdevice 37, to the sight light 20, and to the sight light indicator light34. The power supply is also connected to the motor of the calibrateddrum 30, which is in turn connected to two indicator lights 35 and 36 onthe instrument panel. The

dome 26 of the laser receiver 16 is also connected to on/off switch 33.

In operation, the pilot positions himself utilizing the closed circuittelevision system. The viewing console with screen 19 is mountedadjacent the instrument panel for easy line-of-vision requiring aminimum of eye movement by the pilot from the RPM indicator. It ispreferred that cross-hairs be placed on the console face to assist thepilot in positioning the helicopter over the station mark 11. Two-wayradio communication between the pilot and a man on the ground may alsobe used as an alternative positioning method.

As the helicopter manoeuvres over the survey point the dome 26 receivesthe laser beam from laser 25, and the beam will first fall on at leastone of the outer row of detection cells 27. This will produce no changesince the switch 33 will already be in the off position. When the laserbeam is detected by one of the inner row of cells 28, indicating thatthe helicopter is positioned vertically above the beam of laser 25,switch 33 closes and sight light 20, indicator light 34, and distancemeasuring equipment 37 will be turned on. If the helicopter drifts offfrom the vertical, one of the outer row of detection cells 27 will betriggered opening switch 33 and positively discontinuing operation ofequipment 37 and lights 20 and 34. The turning on and off of switch 33in response to signals generated by the detection cells can be used toinitiate and terminate indicator lights, a sight light, and horizontaland vertical distance measuring equipment.

Indicator light 35 may be a green light and indicator light 36 a redlight. They are controlled by a tension spring in the line 13, with thegreen light 35 being on until the plumb bob 14 touches the ground, atwhich time the green light 35 goes out and the red light 36 comes on.These two lights are in the pilots line of sight, either on thehelicopter instrument panel or on top of the television viewing console.These lights optionally could be eliminated or verified by the use of atwo-way radio on the occasions where a man is stationed on the ground bythe station mark.

We claim:

1. Target positioning apparatus for use in aerial surveying comprising ahelicopter, a closed-circuit television system including a camera and aviewing console both mounted on said helicopter, the camera of saidtelevision system being directed to scan the terrain beneath thehelicopter when it is airborne and the viewing console of saidtelevision system being positioned such that it can be seen by the pilotof the helicopter, and laser alignment means for indicating when saidhelicopter is positioned vertically over a point whose location it isdesired to fix by survey, said laser alignment means including a lasercapable of projecting a laser beam directed vertically between saidhelicopter and said point, and a laser detector for detecting the laserbeam, one of said laser and said laser detector being mounted on saidhelicopter, and means for indicating to the pilot when the laser beam isaligned with said laser detector.

2. Target positioning apparatus as defined in claim 1 wherein said laseris mounted on said helicopter so as to project the laser beam verticallydownward onto the terrain such that its position relative to said pointcan be observed.

3. Target positioning apparatus as defined in claim 1 wherein said laseris positioned over said point in such a manner as to project the laserbeam vertically upward from said point, said laser beam detector beingmounted on said helicopter.

4. Target positioning apparatus as defined in claim 1 wherein saidtelevision camera is mounted on said helicopter such that it canmaintain an attitude substantially vertical to the earth when thehelicopter is airborne and manoeuvring above said point.

5. Target positioning apparatus as defined in claim 3 wherein saidtelevision camera is mounted on said helicopter such that it canmaintain an attitude substantially vertical to the earth when thehelicopter is airborne and manoeuvring above said point.

6. Target positioning apparatus as defined in claim 2 wherein saidtelevision camera is mounted on said helicopter such that it canmaintain an attitude substantially vertical to the earth when thehelicopter is airborne and manoeuvring above said point and wherein saidlaser is mounted on said television camera.

7. Target positioning apparatus as defined in claim 3 wherein saidtelevision camera is mounted on said helicopter such that it canmaintain an attitude substantially vertical to the earth when thehelicopter is airborne and manoeuvring above said point, and whereinsaid laser beam detector is mounted on said television camera.

8. Target positioning apparatus as defined in claim 5 further includinga height measuring device associated with said helicopter capable ofaccurately determining the distance between the hovering helicopter andsaid point.

9. Target positioning apparatus as defined in claim 5 further includinghorizontal distance measuring equipment associated with said helicopter.

10. Target positioning apparatus as defined in claim 5 includinghorizontal distance measuring equipment associated with said helicopterand further including a height measuring device associated with saidhelicopter capable of accurately determining the distance between thehovering helicopter and said point.

11. Target positioning apparatus as defined in claim 7 wherein saidlaser beam detector is capable of activating preselected mechanismsassociated with said helicopter upon detection of the laser beamprojected vertically upward from beneath the helicopter.

12. Target positioning apparatus as defined in claim 7 includinghorizontal distance measuring equipment associated with said helicopter,and wherein said laser beam detector is adapted to activate saidhorizontal distance measuring equipment upon detection of the laser beamprojected vertically upward from beneath the helicopter.

13. Target positioning apparatus as defined in claim 7 wherein saidlaser beam detector comprises two detection cells, and wherein means forperforming an operating function in response to energisation of eitherof said detector cells upon detection of the laser beam by saiddetection cells are connected therewith.

14. Target positioning apparatus as defined in claim 7 wherein saidlaser beam detector comprises plural detection cells, at least one ofsaid cells being so mounted on said helicopter that upon sensingimpingement of said laser beam thereon it is capable of indicating thatthe helicopter is positioned accurately over said point, at leastanother of said cells being so mounted on said helicopter that uponsensing impingement of said laser beam thereon it is capable ofindicating that the helicopter is not positioned accurately over saidpoint.

15. Target positioning apparatus as defined in claim 7 includinghorizontal distance measuring equipment associated with said helicopter,and wherein said laser beam detector comprises plural detection cells, afirst of said cells being adapted to initiate operation of saidhorizontal distance measuring equipment in response to impingement ofthe laser beam on said first cell, and a second one of said cells beingadapted to discontinue operation of said horizontal distance measuringequipment in response to impingement of the laser beam on said secondcell.

16. Target positioning apparatus as defined in claim 7 includinghorizontal distance measuring equipment copter is not positionedaccurately over said point.

1. Target positioning apparatus for use in aerial surveying comprising ahelicopter, a closed-circuit television system including a camera and aviewing console both mounted on said helicopter, the camera of saidtelevision system being directed to scan the terrain beneath thehelicopter when it is airborne and the viewing console of saidtelevision system being positioned such that it can be seen by the pilotof the helicopter, and laser alignment means for indicating when saidhelicopter is positioned vertically over a point whose location it isdesired to fix by survey, said laser alignment means including a lasercapable of projecting a laser beam directed vertically between saidhelicopter and said point, and a laser detector for detecting the laserbeam, one of said laser and said laser detector being mounted on saidhelicopter, and means for indicating to the pilot when the laser beam isaligned with said laser detector.
 2. Target positioning apparatus asdefined in claim 1 wherein said laser is mounted on said helicopter soas to project the laser beam vertically downward onto the terrain suchthat its position relative to said point can be observed.
 3. Targetpositioning apparatus as defined in claim 1 wherein said laser ispositioned over said point in such a manner as to project the laser beamvertically upward from said point, said laser beam detector beingmounted on said helicopter.
 4. Target positioning apparatus as definedin claim 1 wherein said television camera is mounted on said helicoptersuch that it can maintain an attitude substantially vertical to theearth when the helicopter is airborne and manoeuvring above said point.5. Target positioning apparatus as defined in claim 3 wherein saidtelevision camera is mounted on said helicopter such that it canmaintain an attitude substantially vertical to the earth when thehelicopter is airborne and manoeuvring above said point.
 6. Targetpositioning apparatus as defined in claim 2 wherein said televisioncamera is mounted on said helicopter such that it can maintain anattitude substantially vertical to the earth when the helicopter isairborne and manoeuvring above said point and wherein said laser ismounted on said television camera.
 7. Target positioning apparatus asdefined in claim 3 wherein said television camera is mounted on saidhelicopter such that it can maintain an attitude substantially verticalto the earth when the helicopter is airborne and manoeuvring above saidpoint, and wherein said laser beam detector is mounted on saidtelevision camera.
 8. Target positioning apparatus as defined in claim 5further including a height measuring device associated with saidhelicopter capable of accurately determining the distance between thehovering helicopter and said point.
 9. Target positioning apparatus asdefined in claim 5 further including horizontal distance measuringequipment associated with said helicopter.
 10. Target positioningapparatus as defined in claim 5 including horizontal distance measuringequipment associated with said helicopter and further including a heightmeasuring device associated with said helicopter capable of accuratelydetermining the distance between the hovering helicopter and said point.11. Target positioning apparatus as defined in claim 7 wherein saidlaser beam detector is capable of activaTing preselected mechanismsassociated with said helicopter upon detection of the laser beamprojected vertically upward from beneath the helicopter.
 12. Targetpositioning apparatus as defined in claim 7 including horizontaldistance measuring equipment associated with said helicopter, andwherein said laser beam detector is adapted to activate said horizontaldistance measuring equipment upon detection of the laser beam projectedvertically upward from beneath the helicopter.
 13. Target positioningapparatus as defined in claim 7 wherein said laser beam detectorcomprises two detection cells, and wherein means for performing anoperating function in response to energisation of either of saiddetector cells upon detection of the laser beam by said detection cellsare connected therewith.
 14. Target positioning apparatus as defined inclaim 7 wherein said laser beam detector comprises plural detectioncells, at least one of said cells being so mounted on said helicopterthat upon sensing impingement of said laser beam thereon it is capableof indicating that the helicopter is positioned accurately over saidpoint, at least another of said cells being so mounted on saidhelicopter that upon sensing impingement of said laser beam thereon itis capable of indicating that the helicopter is not positionedaccurately over said point.
 15. Target positioning apparatus as definedin claim 7 including horizontal distance measuring equipment associatedwith said helicopter, and wherein said laser beam detector comprisesplural detection cells, a first of said cells being adapted to initiateoperation of said horizontal distance measuring equipment in response toimpingement of the laser beam on said first cell, and a second one ofsaid cells being adapted to discontinue operation of said horizontaldistance measuring equipment in response to impingement of the laserbeam on said second cell.
 16. Target positioning apparatus as defined inclaim 7 including horizontal distance measuring equipment associatedwith said helicopter, said first cell being adapted to initiateoperation of said height measuring device.
 17. Target positioningapparatus as defined in claim 7 wherein said laser beam detectorcomprises two concentric rows of detection cells, the inner row of saiddetection cells upon impingement of said laser beam thereon beingcapable of indicating that the helicopter is positioned accurately oversaid point, the outer row of said detection cells upon impingement ofsaid laser beam thereon being capable of indicating that the helicopteris not positioned accurately over said point.